In general, a Gas Insulated Switchgear (GIS) corresponds to a device that is provided to a power transmission line or a power distribution line to open and close a line in a normal state and in an abnormal state, for example, a ground, a short, and the like, thereby safely protecting a power system.
In the GIS, a composite bushing used by filling sulphur hexafluoride (SF6) gas therein generally includes a flange and a fiberglass reinforced plastics (FRP) tube and a silicon rubber to be inserted into the flange.
To enhance the air-tightness of the sulphur hexafluoride (SF6) gas, the inner circumferential surface of the flange may be processed to be rough. In this case, an adhesive surface may be worn out or be damaged due to a temperature change. Accordingly, there may be some constraints in maintaining the gas air-tightness.
When a discharge is initiated in a bushing that is one of constituent parts of the GIS, wideband electromagnetic waves may occur. In the case of a partial discharge, a cause of the partial discharge may be removed whereby the partial discharge may disappear over time. However, in many cases, a number of times of discharge, a discharge strength, and the like, may increase, which may result in generating a flashover. Here, the flashover indicates a phenomenon that a sparkler instantaneously occurs and thereby current flows.
Accordingly, when the partial discharge of the GIS in operation is measured outside, it is possible to prevent the flashover from occurring and an ultra high frequency (UHF) of a partial discharge measurement sensor has been employed as such measurement unit.
Even though the partial discharge of the bushing needs to be measured by providing the above UHF sensor to the bushing, it may be difficult to install the UHF sensor in a bushing that is generally formed in a magnetism type or an insulator type.
Also, even in the case of using the composite bushing, the composite bushing may be externally exposed and thus, there are some constraints on an area required to install the UHF sensor. Due to noise around the composite bushing, it may be difficult for the UHF sensor to accurately measure the partial discharge.
Also, when the partial discharge of the composite bushing continues, flashover may explode the bushing and injury to personnel may occur.